1. Field of the Invention
The present invention relates to a thermal transfer dye image-receiving sheet. More particularly, the present invention relates to a thermal transfer dye image-receiving sheet (hereinafter referred to as an image-receiving sheet) usable for a thermal imaging printer, especially a dye thermal transfer printer, and capable of printing thermally transferred continuous full-color dye images at a high speed with a high reproducibility, without a thermal curling thereof.
2. Description of the Related Art
Currently there is an enormous interest in the development of new types of thermal transfer dye printers capable of printing clear full colored images or pictures.
In the operation of the thermal transfer dye printers, an image receiving sheet having a image-receiving layer comprising a dye-dyeable resin is superimposed on a dye sheet having a sublimating dye layer, in such a manner that the image-receiving layer of the image-receiving sheet comes into contact with the sublimating dye layer of the dye sheet, and the dye sheet is locally heated imagewise by a thermal head in accordance with electric signals corresponding to the images or pictures to be printed, to thus thermally transfer the dye images or pictures having a color density corresponding to the amount of heat applied to the dye sheet superimposed on the image-receiving sheet.
It is known that a bi-axially oriented thermoplastic resin film comprising a thermoplastic resin, for example, a polyolefin resin, and having a plurality of fine voids or pores is used as a support sheet of an image-receiving sheet, to print thermally transferred dye images having a high picture quality on the image-receiving sheet at a high speed.
In the image receiving sheet, an image-receiving layer comprising, as a main component, a dyeable resin, is formed on the support sheet.
The image-receiving sheet having the above-mentioned support sheet is advantageous in that the resulting image-receiving sheet has a relatively high uniformity in the thickness thereof, and a high flexibility and a low heat-conductivity in comparison with that of a customary paper sheet comprising cellulose pulp fibers, and thus is beneficial in that the resultant thermally transferred dye images thereon are uniform and have a high color density.
Nevertheless, when the bi-axially oriented thermoplastic resin film is utilized as a support sheet of an image-receiving sheet which should exhibit a high reproducibility of the images, the support sheet is disadvantageous in that the void structure in the surface portion of the support sheet causes undesirable fine noise to be created in the recorded images. Also the bi-axially oriented thermoplastic resin film is disadvantageous in that, when thermally printed, the thermoplastic resin film is released from a residual orienting stress thereof created by the orienting process applied to the film and thus shrinks, and this shrinkage causes the image-receiving sheet to be curled or wrinkled. The curling and wrinkling hinder the smooth travel of the image-receiving sheets within the printer, and sometimes cause an undesirable blockage of the sheets.
To eliminate the above-mentioned disadvantages, i.e., creation of curls and wrinkles, attempts have been made to utilize a laminate sheet composed of a core sheet having a relatively small thermal shrinkage or a relatively high modulus of elasticity and oriented thermoplastic resin film layers laminated on the two surfaces of the core sheet, as a support sheet of an image-receiving sheet. Such an attempt is disclosed in U.S. Pat. No. 4,774,224. This type of support sheet, however, is disadvantageous in that the price thereof is too high, and in that since the two laminated film layers each have a different thermal shrinkage rate, the resultant image-receiving sheet is not completely free from a curling thereof due to the difference in the thermal shrinkage of the two laminated film layers when heated.
Also, to eliminate the fine noise from the recorded images, an attempt has been made to utilize, as a support sheet, an oriented film having a high surface smoothness or a laminated composite film prepared therefrom. This attempt is disclosed in U.S. Pat. No. 4,778,782.
The high smoothness film unavoidably exhibits a high glossiness, and thus when the high smoothness film is used as a support sheet of an image-receiving sheet, the resultant images received on the image-receiving sheet exhibit an unnatural glossiness, i.e., an undesirable glitter appearance, and thus have a low value as high reproduction quality images.
Furthermore, since the thermal dye transfer printer is used for full color printing and for video printing, in which the dye images are transferred by a large amount of heat, the image-receiving sheet must record clear images thereon, without a thermal curling and wrinkling, and be able to be industrially supplied under stable conditions.